FINITE ELEMENT MODEL FOR PREDICTING RESIDUAL STRESSES IN SHIELDED METAL ARC WELDING OF MILD STEEL PLATES

This study investigates the prediction of residual stresses developed in shielded metal arc welding of ASTM A36 mild steel platesvia simulation and experiments. The specific objectives were to simulate the shielded manual metal arc welding process by using the finite element method in ANSYS Multiphysics Version 14, to produce experimental samples of butt welded ASTM A36 mild steel plates, to determine the residual stresses developed in the weldment of the steel plates and those generated from the Finite Element Model Simulation, and to establish correlation between experimental and predicted values of residual stress. Findings indicate that the maximum temperature was 1827°C while that at the end of the plate was maintained at around 27°C. From the Finite Element Model Simulation, the transverse residual stress in the x direction (σx) had a maximum value of 375MPa (tensile) and minimum value of -183MPa (compressive) while in the y direction (σy), the maximum value of 172MPa (tensile) and minimum value of 0.The longitudinal stress in the x direction (σx) indicated a maximum value of 355MPa (tensile) and a minimum value of -10MPa (compressive) while in the y direction (σy), the maximum value was 167MPa and the minimum value of the residual stress was -375MPa. The experimental values as measured by the X-Ray diffractometer were similar as transverse residual stress (σx) along the weld line in the transverse x directionvaried from 353MPa (tensile) to – 209MPa (compressive) while in the y direction, stress (σy) along the weld line varied from 177MPa (tensile) to 0. The longitudinal stress measured by the X-Ray diffractometer in the x direction (σx) varied from 339MPa (tensile) to 0 (compressive) while in the y direction (σy) varied from 171MPa (tensile) to -366MPa (compressive). The result of the correlation coefficient test between the experimental and finite element results of residual stresses the was close to unity (1) which indicates a positive uphill linear relationship. The result of the F-Test conducted was also close to unity (1) which indicates the level of variance between the experimental and finite element results of residual stresses was not significant. Based on these results, it was established that using the 3D FEM analysis, results of residual stresses obtained was in good agreement with the experiment.

The use of the Finite Element Method (FEM) in product development is now well

establishedhowever, its use in manufacturing processes is not very common and is part of the field of new applications in computational mechanics. The most important reason for this development is the industrial need to improve productivity and quality of products and to have better understanding of the influence of different process parameters. The modelled phenomena play an important role at various stages of the production of steel parts, for example, welding, heat treatment and casting, among others.

The importance of these applications lies in determining the evolution of stresses and deformations to predict, for example, susceptibility to cracking and thus prevent failures during manufacturing or even service. Furthermore, this simulation tool can be used to optimize some aspects of the manufacturing process.Welding is defined by the American Welding Society (AWS) as a localized coalescence ofmetals or non-metals produced by either heating of the materials to a suitable temperature with or without the application of pressure, or by the application of pressure alone, with or without the use of filler metal (Mackerle, 2004). Welding techniques are one of the most important and most often used methods for joining pieces in industry. Any information about the shape, size and residual stress of a welded piece is of particular interest to improve quality.

The analysis of welding processes involves several branches of Physics, and requires thecoupling of different models addressed to describe the behaviour of a phenomenological system.